Sheet feeding apparatus and image forming apparatus

ABSTRACT

A sheet feeding apparatus includes: a sheet containing device for housing sheets; a sheet feeding roller that feed the sheets contained in the sheet containing device; a pushing member for pushing the sheets contained in the sheet containing device against the sheet feeding roller; a separation pad which is provided so as to be capable of abutting against the sheet feeding roller and separates the sheets one by one as the sheets are fed by the sheet feeding roller and the pushing member; and a sheet guide portion arranged between a pushing portion where the sheets are pushed against the sheet feeding roller by the pushing member and an abutting portion where the sheet feeding roller and the separation pad come into abutment against each other. As a result, a sheet feeding apparatus with reduced noise can be realized. In addition, an image forming apparatus with silent operation can be realized by using the sheet feeding apparatus.

This application claims priority from Japanese Patent Application No. 2003-190395 filed on Jul. 2, 2003, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus that is provided in an image forming apparatus for forming an image on a recording medium such as an electrophotographic copying machine, a printer, a word processor, or a facsimile apparatus.

2. Related Background Art

A sheet feeding apparatus for automatically feeding a recording medium (hereinafter referred to as sheet) to an image forming portion is mounted on an image forming apparatus. FIGS. 13 to 16 show an example of a conventional image forming apparatus and a sheet feeding apparatus mounted on this image forming apparatus.

FIG. 13 is a schematic sectional view of a laser beam printer (hereinafter referred to as printer) 1 that is a conventional image forming apparatus. FIG. 14 is a sectional view of a sheet feeding apparatus mounted on the printer 1, FIG. 15 is a perspective view of the sheet feeding apparatus, and FIG. 16 is an enlarged view of a separating portion of the sheet feeding apparatus.

In FIG. 13, the printer 1 includes: a sheet feeding apparatus 2; and a first conveying roller pair 7 and a second conveying roller pair 9 for conveying a sheet P delivered from the sheet feeding apparatus 2 to an image forming portion F. The image forming portion F includes: a process cartridge 13; a laser scanning optical system 11 for forming an electrostatic latent image on a photosensitive drum 14 that is provided in the process cartridge 13; a transferring roller 15 for transferring a toner image that is formed on the photosensitive drum 14 by developing the electrostatic latent image; and a fixing device 17 for fixing the toner image on the sheet having the toner image transferred thereon.

The transferring roller 15 transfers the toner image, which is formed on the photosensitive drum 14 of the process cartridge 13, to the sheet P conveyed by the first conveying roller pair 7 and the second conveying roller pair 9. The fixing device 17 fixes the toner image to the sheet P by heating and pressurizing the sheet P having the toner image transferred thereon, thereby performing image formation.

Provided on the downstream side of the fixing device 17 are a delivery roller pair 19 for delivery of the sheet P to which the toner image has been fixed and a delivery tray 21 for stacking and receiving sheets to be delivered.

In FIGS. 14 and 15, the sheet feeding apparatus 2 includes: a sheet feeding roller 4 constituted by a semicircular rubber roller 4 a and a shaft 4 b; a pair of sheet feeding sub-rollers 23 that are rotatably held by the shaft 4 b and arranged on both sides of the rubber roller 4 a; and a sheet feeding cassette 3 that houses the sheets P to be supplied to the image forming portion F.

The sheet feeding cassette 3 includes: a cassette main body 3 a; a pressure plate 5 serving as pushing means for supporting the sheets P which is rotatably supported by the cassette main body 3 a; a pressure spring 24 that urges the pressure plate 5 so as to push the leading edge side of the supported sheets P against the sheet feeding roller 4; a separation pad 6 for separating the sheets P, which are delivered by the sheet feeding roller, one by one; a separation spring 25 that urges the separation pad 6 toward the sheet feeding roller 4; width regulating plates 27 and 28 that regulate a position in a width direction of the sheets P contained in the sheet feeding cassette 3; and a trailing edge regulating plate 29 that regulates a position of a trailing edge of the sheets P.

The width regulating plates 27 and 28 provided in the sheet feeding cassette 3 are provided so as to be movable in a width direction of sheets according to a size of the sheets in the sheet feeding cassette 3 in order to regulate a sheet width of the sheets P. The trailing edge regulating plate 29 is provided so as to be movable in the longitudinal direction of the sheets according to the size of the sheets.

The separation pad 6 is constituted by a rubber material 6 a, which comes into abutment against the sheet feeding roller 4, and a holder 6 b, which is rotatably held by the cassette body 3 a that holds the rubber material 6 a. The separation pad 6 is urged by the separation spring 25 such that the rubber material 6 a is brought into press-contact with the sheet feeding roller 4. The separation pad 6 comes into abutment against outer peripheral surfaces of the sheet feeding sub-rollers 23 in a sheet feed standby state, and is pushed against the outer peripheral surfaces of the sheet feeding sub-rollers 23 through the sheet P during conveyance of the sheet P.

However, the conventional sheet feeding apparatus disclosed in Japanese Patent Application Laid-Open No. 08-157110 has a problem in that a trailing edge of a sheet that is fed after being separated jumps as the sheet passes through the separation pad, thus generating noise. In order to solve this problem, there is a technique for providing wing portions at both ends of the separation pad in a direction perpendicular to a sheet conveying direction.

However, the technique disclosed in the laid-open patent application only addresses the problem of trailing edge jumping sound that is caused as the trailing edge of the separated sheet jumps after passing through a press-contact portion between the sheet feeding roller and the separation pad. The technique does not address the problem of trailing edge jumping sound that is caused when the trailing edge of the separated sheet moves away from a sheet stacking portion.

That is, in the sheet feeding apparatus shown in FIG. 16, an abutting portion N2, where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, is arranged adjacent to a pushing portion N where the sheets P are pushed against the sheet feeding roller 4 by the pressure plate 5 (abutting portion where the sheet feeding roller 4 and the sheet P come into abutment against each other) and on the downstream side with respect to the sheet conveying direction. A trailing edge P1 of the sheets P to be fed jumps in a direction of arrow A immediately after passing through the pushing portion where the sheets P are pushed against the sheet feeding roller 4 by the pressure plate 5, and hits the separation pad 6 to generate trailing edge jumping sound. In particular, this trailing edge jumping sound becomes more noticeable with a stiff sheet such as thick sheet, causing deterioration in the noise level of the printer 1. Thus, it is necessary to reduce the trailing edge jumping sound for the purpose of achieving a silent operation.

SUMMARY OF THE INVENTION

The present invention has been devised in order to solve the above-mentioned problems, and it is an object of the present invention to realize a sheet feeding apparatus with reduced noise and provide an image forming apparatus capable of silent operation.

To attain the above object, according to the present invention, there is provided a sheet feeding apparatus characterized by including: sheet housing means for housing sheets; a sheet feeding roller for feeding the sheets housed in the sheet housing means; pushing means for pushing the sheets against the sheet feeding roller; a separation pad that comes into abutment against the sheet feeding roller and separates the sheets one by one as the sheets are fed by the sheet feeding roller and the pushing means; and a sheet guide portion that is arranged between a pushing portion where the sheets are pushed against the sheet feeding roller by the pushing means and an abutting portion where the sheet feeding roller and the separation pad come into abutment against each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an image forming apparatus including a sheet feeding apparatus in accordance with a first embodiment of the present invention;

FIG. 2 is a schematic sectional view of the sheet feeding apparatus in accordance with the first embodiment of the present invention;

FIG. 3 is a perspective view of a sheet feeding cassette included in the sheet feeding apparatus in accordance with the first embodiment of the present invention;

FIG. 4A is a partial sectional view of the sheet feeding apparatus in accordance with the first embodiment in a state where the sheet feeding apparatus is fully loaded with sheets;

FIG. 4B is a partial sectional view of the sheet feeding apparatus in accordance with the first embodiment of the present invention in a state where the sheet feeding apparatus is loaded with a small amount of sheets;

FIG. 5 is a partial sectional view showing attachment angles of respective members of the sheet feeding apparatus in accordance with the first embodiment of the present invention;

FIG. 6 is a partial sectional view of the sheet feeding apparatus in accordance with the first embodiment of the present invention in a sheet feeding operation;

FIG. 7 is a partial sectional view of the sheet feeding apparatus in accordance with the first embodiment of the present invention in a conveying operation;

FIG. 8 is a schematic sectional view of a sheet feeding apparatus in accordance with a second embodiment of the present invention;

FIG. 9 is a perspective view of a sheet feeding cassette included in the sheet feeding apparatus in accordance with the second embodiment of the present invention;

FIG. 10 is a partial sectional view of a sheet feeding apparatus in accordance with a third embodiment of the present invention;

FIG. 11 is a partial sectional view of a sheet feeding apparatus in accordance with a fourth embodiment of the present invention;

FIG. 12 is a perspective view of a sheet feeding cassette included in the sheet feeding apparatus in accordance with the fourth embodiment of the present invention;

FIG. 13 is a schematic sectional view of an image forming apparatus including a conventional sheet feeding apparatus;

FIG. 14 is a schematic sectional view of the conventional sheet feeding apparatus;

FIG. 15 is a schematic perspective view of the conventional sheet feeding apparatus; and

FIG. 16 is a view for explaining a problem of the conventional sheet feeding apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

A first embodiment of a sheet feeding apparatus of the present invention will be explained below with a laser beam printer, which is an image forming apparatus adopting an electrophotographic system, as an example.

FIG. 1 is a sectional view of a laser beam printer (hereinafter referred to as printer) 1. FIG. 2 is a sectional view of a sheet feeding apparatus mounted on this printer 1. FIG. 3 is a perspective view of a sheet feeding cassette that is mounted on the sheet feeding apparatus shown in FIG. 1. A structure of the printer 1 will be explained with reference to these figures.

(Image Forming Portion)

In FIG. 1, an image forming portion F includes: a process cartridge 13 that is constituted by a photosensitive member 14, and a developing device, a cleaner, a charging roller, and the like, which are not shown in the figure; a transferring roller 15 that transfers a visualized image on the photosensitive member 14 onto a sheet P; and a fixing device 17 that heats and fixes the visualized image on the sheet P. Note that reference numeral 16 denotes a conveyance guide that guides the sheet P to which the image has been transferred to the fixing device 17.

(Laser Scanner)

As shown in FIG. 1, the laser scanner 11 is arranged so as to be slanted upward to the right from a scanner polygon 11 a. Here, in order to reduce a size of the printer 1 as much as possible, it is most effective to cause a laser beam to be incident on the photosensitive member 14 with a return mirror 12 from a direction substantially perpendicular to a horizontal conveying path for sheets extending from the transferring roller 15 to the fixing device 17 as shown in FIG. 1. Such a structure makes it possible to keep a depth and a height of the printer 1 within minimum dimensions.

(Sheet Conveying Path)

As shown in FIG. 1, the sheet feeding cassette 3 is arranged in a lower part of a main body of an image forming apparatus (hereinafter referred to as printer main body) 1 a. A delivery tray 21 is formed integrally with an outer cover 20 in an upper part of the printer body 1 a. The sheet feeding cassette 3 and the delivery tray 21 are coupled to each other by a sheet conveying path including the image forming portion F. This sheet conveying path constitutes an S-shaped path as a whole. The sheet feeding cassette 3 is arranged in the lower part of the printer body 1 a, and the delivery tray 21 is arranged in the upper part of the printer body 1 a to form the S-shaped sheet conveying path in this way, whereby the printer 1 is made compact to reduce an installation area.

A sheet delivered from the sheet feeding cassette 3 is sent to the image forming portion F by a curved sheet conveying path 8. A first conveying roller pair 7 and a second conveying roller pair 9 are arranged in the sheet conveying path 8, and the sheet is conveyed to the image forming portion F by these sheet conveying roller pairs 7 and 9. In the first conveying roller pair 7, a direction of a nip line thereof (a tangent of a press-contact portion of a roller) is a vertical direction. The first conveying roller pair 7 conveys a sheet delivered from a sheet feeding apparatus 2, which will be described later in detail, in the vertical direction. The sheet to be conveyed is guided to the second conveying roller pair 9 by the curved sheet conveying path 8.

Reference numeral 10 denotes a registration sensor. This registration sensor 10 synchronizes a leading edge position of a sheet P, which is conveyed by the sheet conveying roller pairs 7 and 9, with light-emitting timing of the laser scanner 11 serving as an exposure light source and starts drawing an image from a predetermined position on the sheet P.

A sheet discharge sensor 18 for detecting a leading edge position and a trailing edge position of the sheet P, which has been heated and fixed by the fixing device 17, and detecting jam is provided in a sheet conveying path 8 on a downstream side of the image forming portion F. In addition, a sheet discharge roller pair 19 for delivery of the sheet P onto a delivery tray 21 is provided on a downstream-side end of the sheet conveying path 8B.

(Electrical Components Layout)

Reference numeral 22 denotes an electrical portion consisting of an AC power supply and a DC power supply, and a high voltage power supply. As shown in FIG. 1, the electrical portion 22 is arranged below a horizontal conveying path extending from the transferring roller 15 to the fixing device 17 and above the sheet feeding cassette 3, whereby the space of the printer body 1 a is used efficiently to prevent an increase in installation area due to the electrical portion 22. In addition, by arranging the electrical portion 22 below the horizontal conveying path extending from the transferring roller 15 to the fixing device 17, bundle wires necessary for electrical connection of the transferring roller 15 and the fixing device 17 can be simplified.

(Sheet Feeding Apparatus)

In FIGS. 2 and 3, the sheet feeding apparatus 2 includes: a sheet feeding portion 2 a that is provided in the printer body 1 a; and a sheet feeding cassette 3 that houses sheets to be delivered by the sheet feeding portion 2 a. The sheet feeding portion 2 a includes: a sheet feeding roller 4, which is constituted by a semicircular rubber roller 4 a and a shaft 4 a, attached to the printer body 1 a; and sheet feeding sub-rollers 23 that are rotatably held by the shaft 4 b and arranged on both sides of the rubber roller 4 a. The sheet feeding sub-rollers 23 are set to have an outer diameter smaller than a maximum outer diameter of the semicircular rubber roller 4 a.

The sheet feeding cassette 3 for housing the sheets P includes: a pressure plate 5 serving as pushing means for pushing a leading edge side of the housed sheets P against the sheet feeding roller 4; a pressure spring 24 that urges the pressure plate 5 upward; width regulating plates 27 and 28 that regulate a position in a width direction of the sheets P stacked on the pressure plate 5; and a trailing edge regulating plate 29 that regulates a trailing edge position of the sheets P. The width regulating plates 27 and 28 are movable in a width direction of the sheets P according to a size of the sheets P in order to regulate a width of the sheets P, and the trailing edge regulating plate 29 is movable in a length direction of the sheets P according to the size of the sheets P.

Moreover, the sheet feeding cassette 3 includes: a separation pad 6 for separating the sheets P, which are delivered by the sheet feeding roller 4, one by one; and a separation spring 25 that urges the separation pad 6 to the sheet feeding roller 4. Between a pushing portion N1 where the sheets P are pushed against the sheet feeding roller 4 by the pressure plate 5 (abutting portion where the sheet P and the sheet feeding roller 4 come into abutment against each other) and an abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, a sheet guide surface 26, which guides the sheets P delivered by the sheet feeding roller 4 toward the abutting portion N2, is formed integrally with a cassette body 3 a.

The pressure plate 5 is held in the sheet feeding cassette 3 so as to be rotatable about a rotation center 5A and pushes the leading edge side of the sheets P against the sheet feeding sub-rollers 23 by a spring force of the pressure spring 24 in a sheet feed standby state. A separation sheet 30 (shown in FIG. 3) is provided in a part of the pressure plate 5 opposed to the sheet feeding roller 4. The separation sheet 30 consists of cork, synthetic resin, or the like and prevents double feeding of the lowermost sheet P stacked on the sheet feeding cassette 3.

The separation pad 6 consists of a rubber material 6 a, which comes into abutment against the sheet feeding roller 4, and a holder 6 b, which holds the rubber material 6 a. The separation pad 6 comes into abutment against the sheet feeding sub-rollers 23 in a sheet feed standby state, and is pushed against the sheet feeding sub-rollers 23 through the sheet P during conveyance of the sheets P fed to the sheet conveying path 8 by the sheet feeding roller 4. The separation pad 6 and the separation spring 25, which urges the separation pad 6, are provided in the cassette body 3 a.

The sheet feeding cassette 3 is detachably mounted on the printer body 1 a. Thus, when the sheets P are supplied, the sheet feeding cassette 3 can be removed from the image forming apparatus body 1 a to perform supply of additional sheets.

FIG. 4A is a partial sectional view of a sheet feeding apparatus at the time when the sheet feeding apparatus is fully loaded with the sheets P. FIG. 4B is a partial sectional view of the sheet feeding apparatus at the time when the sheet feeding apparatus is loaded with a small amount of the sheets P.

A tangent B of the sheet feeding roller 4 in the pushing portion N1 and a sheet top surface P2 in FIG. 4A coincide with each other. In addition, a tangent C of the sheet feeding roller 4 in the pushing portion N1 and a sheet top surface P3 in FIG. 4B coincide with each other. In this way, the pressure plate 5 is arranged such that a tangent direction of the sheet feeding roller 4 in the pushing portion N1 and a top surface of sheets coincide with each other regardless of the amount of stacked sheets P.

In FIG. 5, when it is assumed that an angle formed by the tangent (nip line) B of the sheet feeding roller 4 in the pushing portion N1 and the sheet guide surface 26 is a, and an angle formed by a tangent (nip line) of the sheet feeding roller 4 in the abutting portion N2 and the sheet guide surface 26 is β, the angles α and β are set so as to satisfy the following two expressions. 110°≦α≦135° 170°≦β≦175°

Table 1 shows a result of an experiment in which the angles α and β are changed. As it is seen from this result, by setting the angles α and β to 110°≦α≦135° and 170°≦β≦175°, satisfactory sheet feeding performance is obtained with thin sheet (60 g sheet) and thick sheet (163 g sheet). When the angles α and β are reduced, a conveying resistance at a leading edge of the sheet P to be fed increases to cause defective sheet feeding. In addition, when the angles α and β are increased, this results in reduced leading-edge separating action for the sheets P to cause double feeding.

In this way, when it is assumed that an angle formed by the tangent B of the sheet feeding roller 4 and the sheet feeding rollers 23 in the pushing portion N1 and the sheet guide surface 26 is a, and an angle formed by the tangent in the abutting portion N2, where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, and the sheet guide surface 26 is β, by setting the angles α and β as 110°≦α≦135° and 170°≦β≦175°, occurrence of defective sheet feeding and double feeding is eliminated, and satisfactory sheet feeding performance is obtained with thin sheet and thick sheet. TABLE 1 (α/β) 110°˜135°/ 110°˜135°/ 110°˜135°/ 140°/ (Sheet type) 105°/165° 1650 170°˜175° 180° 170°˜175°  60 g sheet defective Good Good Good Good Good sheet feeding double Good Good Good Improper Improper feeding Sheet Sheet Feeding Feeding 163 g sheet defective Improper Improper Good Good Good sheet Sheet Sheet feeding Feeding Feeding double Good Good Good Good Good feeding

In addition, when it is assumed that a coefficient of friction between the sheet guide surface 26 and the sheet P is μ1, a coefficient of friction between the separation pad 6 and the sheet P is μ2, and a coefficient of friction between the sheet feeding roller 4 and the sheet P is μ3, the coefficients of friction are set so as to satisfy a relation of μ1<μ2<μ3. In this embodiment, the coefficient of friction μ1 between the sheet guide surface 26 and the sheet P is set to about 0.1 to 0.2, the coefficient of friction μ2 between the separation pad 6 and the sheet P is set to about 0.7 to 1.0, and the coefficient of friction μ3 between the sheet feeding roller 4 and the sheet P is set to about 1.5 to 2.0.

In this way, when it is assumed that a coefficient of friction between the sheet guide surface 26 and the sheet P is μ1, a coefficient of friction between the separation pad 6 and the sheet P is μ2, and a coefficient of friction between the sheet feeding roller 4 and the sheet P is μ3, by setting the coefficients of friction so as to satisfy a relation of μ1<μ2<μ3, there is an effect in that a conveying resistance of the sheet P on the sheet guide surface 26 is reduced to prevent defective sheet feeding. There is also an effect in that separating performance in the abutting portion N2, where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, is improved to prevent double feeding.

(Sheet Feeding Operation)

A sheet feeding operation of the sheet feeding apparatus of the present invention will be explained. FIG. 6 is a partial sectional view of the sheet feeding apparatus in a sheet feeding operation. FIG. 7 is a partial sectional view of the sheet feeding apparatus in a conveying operation.

The sheet feeding roller 4 receives transmission of a drive force from a drive source such as a motor (not shown in the figure) and rotates in a direction of arrow D in FIG. 6. Then, of the sheets P pushed against the sheet feeding roller 4 by the pressure plate 5 due to the force of the pressure spring 24, a few sheets P at the top including the one brought into abutment against the sheet feeding roller 4 are conveyed by the sheet feeding roller 4. Next, a leading edge P4 of the sheets P conveyed by the sheet feeding roller 4 are handled on the sheet guide surface 26, which is formed as an inclined surface inclined toward the abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, whereby the sheets P are subjected to a separating action and separated (hereinafter referred to as first separation). Subsequently, the sheets P, which could not be separated on the sheet guide surface 26, are separated in the abutting portion N2 where the rubber material 6 a of the separation pad 6 and the sheet feeding roller 4 come into abutment against each other, (hereinafter referred to as second separation) to send only one sheet, which is in abutment against the sheet feeding roller 4, to the sheet conveying path 8 so as to be fed to the first conveying roller pair 7.

As shown in FIG. 7, when the sheet feeding roller 4 makes one revolution and stops at a standby position, the sheet P conveyed by the first conveying roller pair 7 is conveyed while being brought into abutment against the sheet feeding sub-rollers 23 by a pushing force of the pressure plate 5 and the separation pad 6. Then, after passing over the pressure plate 5, a trailing edge P5 of the sheet P is led to the abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, while being guided by the sheet guide surface 26.

In the sheet feeding apparatus according to the first embodiment of the present invention, after passing over the pressure plate 5, the trailing edge P5 of the sheet P is led to the abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, while being guided by the sheet guide surface 26. Thus, there is an effect in that generation of trailing edge jumping sound can be reduced.

In addition, the sheets P are subjected to separating actions in two stages consisting of the first separation for handling and separating the sheets P on the sheet guide surface 26 formed as an inclined surface and the second separation for separating the sheets P in the abutting portion N2 where the rubber material 6 a of the separation pad 6 and the sheet feeding roller 4 come into abutment against each other. Thus, there is an effect in that the double feeding preventing effect is improved.

In addition, by setting an angle of the sheet guide surface 26 and an angle of the separation pad 6 to the above-mentioned angles, a sheet is delivered from the sheet feeding cassette 3 substantially in a vertical direction. Thus, the sheets, which are housed horizontally, are rapidly oriented upward and fed in the separating portion of the sheet feeding roller 4 and the separation pad 6 and passed to the sheet conveying path 8 arranged in a vertical direction. In this way, since the horizontally supported sheets can be delivered in the vertical direction, a size in the horizontal direction of the sheet feeding apparatus can be suppressed to realize a reduction in the size of the printer 1.

Second Embodiment

Next, a second embodiment of the sheet feeding apparatus in accordance with the present invention will be explained with reference to FIGS. 8 and 9. Note that only structures and operations different from those in the first embodiment will be explained. The other structures and operations are the same as those in the first embodiment.

FIG. 8 is a sectional view of a sheet feeding apparatus 2 in accordance with the second embodiment. FIG. 9 is a perspective view of a sheet feeding cassette 3 that is mounted on this sheet feeding apparatus.

In the sheet feeding apparatus 2, the inclined guide surface 26, which is provided between the pushing portion N1 where the sheets P are pushed against the sheet feeding roller 4 by the pressure plate 5 and the abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, and which guides the sheets P delivered by the sheet feeding roller 4 toward the abutting portion N2, is formed integrally with the holder 6 b of the separation pad 6.

In this structure, the sheets P are subjected to separating actions in two stages consisting of the first separation for handling and separating the sheets P on the sheet guide surface 26 formed in a slope shape and the second separation for separating the sheets P in the abutting portion N2 where the rubber material 6 a of the separation pad 6 and the sheet feeding roller 4 come into abutment against each other. Thus, there is an effect in that improved double-sheet feeding preventing effect can be attained.

In addition, after passing over the pressure plate 5, the trailing edge P5 of the sheet P is led to the abutting portion N2, where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, while being guided by the sheet guide surface 26. Thus, there is an effect in that generation of trailing edge jumping sound can be reduced.

Third Embodiment

Next, a third embodiment of the sheet feeding apparatus in accordance with the present invention will be explained. FIG. 10 is a main part sectional view of the sheet feeding apparatus in accordance with the third embodiment. Only structures and operations different from those of the first and the second embodiments will be described. The other structures and operations are the same as those in the first and the second embodiments.

In the sheet feeding apparatus 2, the sheet guide surface 26 is formed in an arc shape with an inner diameter surface thereof serving as a sheet guide. The sheet guide surface 26 is provided between the pushing portion N1, where the sheets P are pushed against the sheet feeding roller 4 by the pressure plate 5, and the abutting portion N2, where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, and guides the sheets P delivered by the sheet feeding roller 4 toward the abutting portion N2.

In this structure, a separating action acts on the sheets P, which are conveyed by the sheet feeding roller 4, at a curvature on the sheet guide surface 26 formed in an arc shape toward the abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, and the sheets P are subjected to the first separation.

Subsequently, the sheets P, which could not be separated on the sheet guide 26 are subjected to the second separation in the abutting portion N2, where the rubber material 6 a of the separation pad 6 and the sheet feeding roller 4 come into abutment against each other, to send only one sheet, which is in abutment against the sheet feeding roller 4, to the sheet conveying path 8 so as to be fed to the first conveying roller pair 7.

Thus, the sheets P are subjected to separating actions in two stages consisting of the first separation for separating the sheets P at a curvature on the sheet guide surface 26 formed in an arc shape and the second separation for separating the sheets P in the abutting portion N2 where the rubber material 6 a of the separation pad 6 and the sheet feeding roller 4 come into abutment against each other. Thus, there is an effect in that the double feeding preventing effect is improved.

In addition, after passing over the pressure plate 5, the trailing edge P5 of the sheet P is led to the abutting portion N2 where the sheet feeding roller 4 and the separation pad 6 come into abutment against each other, while being guided by the sheet guide surface 26, similarly to the first embodiment. Thus, there is an effect in that generation of trailing edge jumping sound can be reduced.

Fourth Embodiment

Next, a fourth embodiment of the sheet feeding apparatus in accordance with the present invention will be explained. FIG. 11 is a sectional view of the sheet feeding apparatus in accordance with the fourth embodiment. FIG. 12 is a perspective view of a sheet feeding cassette to be mounted on the sheet feeding apparatus. Only structures and operations different from those in the first to the third embodiments will be explained. The other structures and operations are the same as those in the first to the third embodiments.

The sheet guide surface 26 is constituted by a tabular member of metal, fixed to the sheet feeding cassette 3 by fixing means such as screws or fitting, and grounded. Since the sheet guide surface 26 is constituted by the tabular member of metal and grounded in this way, there is an effect in that wear of the sheet guide surface 26 due to conveyance and sliding of the sheet P is prevented and occurrence of defective sheet feeding and double feeding due to the wear of the sheet guide surface 26 is prevented. In addition, since charging due to sliding of the sheet P and the sheet guide surface 26 can be prevented, there is an effect in that a defective image due to charging is prevented. 

1. A sheet feeding apparatus comprising: sheet containing means for containing sheets; a sheet feeding roller for feeding the sheets contained in said sheet containing means; pushing means for pushing the sheets contained in said sheet containing means against said sheet feeding roller; a separation pad which is provided at a position to be capable of abutting against the sheet feeding roller and separates the sheets one by one as the sheets are fed by the sheet feeding roller and said pushing means; and a sheet guide portion arranged between a pushing portion where the sheets are pushed against the sheet feeding roller by said pushing means and an abutting portion where the sheet feeding roller and the separation pad come into abutment against each other.
 2. A sheet feeding apparatus according to claim 1, wherein the sheet guide portion is formed integrally with said sheet containing means.
 3. A sheet feeding apparatus according to claim 1, wherein the sheet guide portion has as inclined surface that is inclined from the pushing portion where the sheets are pushed against the sheet feeding roller by said pushing means, toward the abutting portion where the sheet feeding roller and the separation pad come into abutment against each other.
 4. A sheet feeding apparatus according to claim 1, wherein the sheet guide portion has an arc shape with an inner diameter surface thereof serving as a sheet guide.
 5. A sheet feeding apparatus according to claim 1, wherein said pushing means rotates about its rotation center to push the sheets against the sheet feeding roller and is arranged with respect to the sheet feeding roller such that a tangent direction of the pushing portion, where the sheets are pushed against the sheet feeding roller by said pushing means, and a direction of a surface on which the sheets pushed against the sheet feeding roller by said pushing means are stacked, coincide with each other.
 6. A sheet feeding apparatus according to claim 1, wherein, when it is assumed that an angle formed by a tangent of the pushing portion, where the sheets are pushed against the sheet feeding roller by said pushing means, and a guide surface of the sheet guide portion is α, and an angle formed by the guide surface of the sheet guide portion and a nip line of the abutting portion, where the sheet feeding roller and the separation pad come into abutment against each other, is β, the angles α and β respectively satisfy a relation of 110°≦α≦135° and a relation of 170°≦β≦175°
 7. A sheet feeding apparatus according to claim 6, wherein the separation pad includes a separating member formed of a rubber material and coming into abutment against the sheet feeding roller to separate the sheets, and a retaining member that retains the separating member, and wherein the sheet guide portion is formed integrally on an upstream side in a sheet conveying direction of the retaining member.
 8. A sheet feeding apparatus according to claim 1, wherein, when it is assumed that a coefficient of friction between a guide surface of the sheet guide portion and the sheets is μ1, a coefficient of friction between the separation pad and the sheets is μ2, and a coefficient of friction between the sheet feeding roller and the sheets is μ3, the coefficients of friction satisfies a relation of μ1<μ2<μ3.
 9. A sheet feeding apparatus according to claim 1, wherein a guide surface of the sheet guide surface is made of metal, and the sheet guide portion is grounded.
 10. A sheet feeding apparatus comprising: a sheet feeding cassette; a sheet feeding roller which comes into abutment against sheets stacked on an intermediate plate provided in a cassette main body of the sheet feeding cassette and rotates to feed the sheets; a separation pad which is provided at a position to be capable of abutting against the sheet feeding roller and separates the sheets one by one as the sheets are delivered by said sheet feeding roller; and a sheet guide portion which is located between a pushing portion, where the sheets are pushed against the sheet feeding roller, and an abutting portion where said sheet feeding roller and the separation pad come into abutment against each other, and is formed integrally with the cassette main body.
 11. A sheet feeding apparatus according to claim 9, wherein, when it is assumed that an angle formed by a tangent of the pushing portion, where the sheets are pushed against the sheet feeding roller by said pushing means, and a guide surface of the sheet guide portion is α, and an angle formed by the guide surface of the sheet guide portion and a nip line of the abutting portion, where the sheet feeding roller and the separation pad come into abutment against each other, is β, the angles α and β respectively satisfy a relation of 110°≦α≦135° and a relation of 170°≦β≦175°
 12. A sheet feeding apparatus according to claim 9, wherein, when it is assumed that a coefficient of friction between a guide surface of the sheet guide portion and the sheets is μ1, a coefficient of friction between the separation pad and the sheets is μ2, and a coefficient of friction between the sheet feeding roller and the sheets is μ3, the coefficients of friction satisfies a relation of μ1<μ2<μ3.
 13. An image forming apparatus comprising: the sheet feeding apparatus according to any one of claims 1 to 12; and an image forming portion that forms an image on the sheets delivered from the sheet feeding apparatus. 